Process of pouring metals and products produced thereby



Patented Jan. 3, 1950 UNITED STATES PATENT PRODUCTS PRODUCED- HolbertEarl Dunn, Crafton, and Heinrich Wilhelm Rathmann, Pittsburgh, Pa., andHoward Calvin Parkman, Niagara Falls, N; Y., assignora to VanadiumCorporation of America, New York, N. Y., a corporation of DelawareApplication August 27, 1946, Serial No. 693,198

14 Claims.

The present invention relates to a process of pouring metals andproducts produced thereby, and more specifically to a process of pouringor casting refractory metals which have smelting slags characterized byhigh viscosity and from which the metals do not readily separate. Theinvention has been developed by us with particular reference to thecasting of ferro-chromium, and will therefore be described withparticular reference thereto.

Figure 1 of the accompanying drawing is an elevation partly in sectionshowing diagrammatically the casting, of high-carbon ferro-chromium andFigure 2 is a similar view showing the casting of low-carbonferro-chromium.

The invention relates particularly to the pouring of molten metalthrough a body of slag of such a character and in such a manner thatmetal of the cast regulus or ingot shows an improved cleanliness and isparticularly free from high melting point non-metallic inclusions. Oneof the principal objects of the invention is to obtain by the processherein described such an improved cleanliness in the cast metal. Anotherobject is the eflicient production of sound ingots having an improvedskin distinguished by freedom from cracks. Other objects of theinvention will be apparent from the following description and claims.

The invention will first be described with particular reference to itsapplication in the production of high-carbon ferro-chromium. Highcarbonferro-chromium is a notable example of a refractory metal which has asmelting slag characterized by high viscosity and from which the moltenhigh-carbon ferro-chromium does not readily separate. High-carbonferro-chromium is produced by the smelting of chromite ore in anelectric furnace, usually an electric arc furnace. Chromite ore,together with coke, coal, and sometimes a small amount of silica as aflux, are added to the top of the furnace as the charge. Thecarbonaceous material reduces the chromite ore to form moltenhigh-carbon ferro-chromium which, together with the slag produced by thesmelting operation, descends into the bottom part of the furnace fromwhich the metal and slag are periodically tapped. High-carbonferrochromium has a melting point in the neighborhood of 2800 F. and isusually tapped at a temperature from about 2900 F. to 3200 F. Even atsuch tapping temperatures the slag is sluggish or highly viscous to drycokey consistency and quickly chills. The ferro-chromium metal does notreadily separate from such slags but appreciable quantities of the metalare entrapped as shot in the usual pouring operation. The usual practicehas been to tap the metal from the furnace, together with as much slagas will run out with the metal, into a refractory lined ladle in whichthe metal is allowed to freeze or from which it may be-drained from aclay-plugged hole in the bottom of the ladle into a suitable chill mold.The smelting slag is so viscous and refractory that it is readilyentrapped in the ferro-chromium, not only in microscopic inclusions butin inclusions of considerable size. It forms slag attachments to thesurface of the metal which are very diflicult to separate afterfreezing. The inclusions are characterized by the presence of numeroushighly refractory polyhedral inclusions of the chromite type. which areparticularly difficult to remove in steelmaking operations and areparticularly objectionable if carried through to the finished steelproduct. The fracture of the cold metal is usually of a dull, silverylustre, often heat-tinted to bluish oxidized surfaces caused byinfiltration of the air through numerous cracks in the surface of theingot, particularly when cast in a chill mould. When the metal isallowed to freeze in the ladle the ingot is characterized by a roughsurface containing large slag attachments which are difficult to removefrom the ingot. When the metal is tapped from the ladle into a chillmold these slag attachments still persist to some extent, and inaddition, the rapid chilling of the metal results in surface strains andsurface cracking so that when removed from the mold the ingot tends tobreak into undesirably small pieces.

We have found that by pouring the ferrochromium through a body ofcasting slag, as hereinafter described, the objectionable inclusionswhich resulted from the refractory smelting slag can be largely, if notcompletely eliminated. Not only are the large inclusions of entrappedslag eliminated, but microscopic inclusions of various objectional typesincluding those of the chromite type which have been particularlyobjectionable in high-carbon ferro-chromium, as heretofore made, arelargely, if not completely, eliminated. The following is a specificexample of our process as applied to the making of high-carbonferrochromium.

The high-carbon ferro-chromium is smelted in the usual electric arcfurnace and the metal and slag are tapped in the usual way, since ourprocess does not require any change in the usual smelting and tappingoperations. The metal and accompanying slag, however, are tapped into aladle containing a previously prepared casting slag. The casting slag isa relatively fluid slag and has a melting point considerably lower thanthat of the smelting slag. The casting slag may be made synthetically ormay be formed by suitable additions from slags of other metallurgicaloperations. We have utilized a. waste slagof another metallurgicaloperation which had the following composition:

Per cent S10: 27.54 CaO 46.44 MgO 18.25 FeO 0.94

CrzOs 0.90

This slag was adjusted and made more fluid by the addition of about 275to 350 pounds of silica sand to about 20 cubic feet of the originalwaste slag. The slag was put into an electric furnace and melted to forma fluid adjusted slag of the following composition:

As we have carried out the process in the making of high-carbonferro-chromium, a furnace tapping high-carbon ferro-chromium at the rateof 3400 pounds per tap (about 8 cubic feet) every one and two-thirdshours was employed and was serviced by a cast iron ladle of about 34cubic feet capacity and weighing about 9300 pounds. About 16 cubic feetof adjusted slag was poured into the ladle, filling it to a depth ofabout 25 inches. The temperature of the adjusted slag was 3000 to 3100F., having a fluidity of to 9.5 inches as measured by the Hertyviscosimeter. The ladle was then transferred to tapping position at thespout of the ferro-chromium smelting furnace about 5 to minutes beforethe tap hole was scheduled to open. This period of time allowed the slagnext to the inner surface of the cast iron ladle to chill, forming athin frozen slag skull over the bottom and sides of the ladle. The ladlein tapping position was placed as high as possible beneath the tappingspout so that the surface of the receiving pool of casting slag wasabout 35 inches below the level of the spout runner. The furnace wasthen tapped and the melted term-chromium, together with as much of thesmelting slag as would flow out with the ferro-chromium, was run intothe ladle. The average time between tapping and plugging of the tap holewas about 8 to 12 minutes with a range of 4 to 20 minutes. Theferro-chromium was tapped at an average temperature of about 3000 to3100" F., but ranged from between 2820 and 3240 F. The thick, viscoussmelting slag ran out at a temperature about to less than thetemperature of the ferro-chromium. Approximately the same volume ofmetal as slag flowed from the furnace, the combined volume of metal andsmelting slag averaging about 14 to 17 cubic feet, depending on thefurnace burden. This casting practice is diagrammatically illustrated inFigure 1 of the drawings in which reference numeral l indicates the castiron ladle, 2 the smelting furnace, 3 the spout of the furnace, 4 thebody of casting slag. 5 the pool of molten metal forming in the bottomof the ladle, 6 the auaaec 4 thin skull of chilled slag between theladle and the ferro-chromium, and l and 8 the metal and the accompanyingsmelting slag respectively flowing from the spout into the ladle.

The deep pool 4 of casting slag into which the metal is teemed has atriple function. It washes the metal and removes slag inclusions whichare present in the metal as tapped from the furnace. It serves to stripthe smelting slag away from the teemed stream of metal and to dissolvethe smelting slag, thus reducing its viscosity and preventing inclusionsof refractory smelting slag, and also releasing particles of metalentrapped in the smelting slag. It serves to check the velocity of themetal as poured from the furnace into the ladle and causes a gentledescent of the metal onto the top of the quiescent accumulating pool ofmetal in the bottom of the ladle.

The slag layer is deep enough so that it has a substantial washingaction on the metal to remove from it slag inclusions present in themetal as it is teemed from the furnace. These inc1usions are highmelting point inclusions characteristic of the high-melting smeltingslag with which the metal was in contact in the furnace. The fluidcasting slag tends to dissolve these inclusions and remove them from themetal.

When the stream of metal and smelting slag enters the layer of castingslag the stream of smelting slag is stripped away from the stream ofmetal, and because of its greater density the metal descends through thecasting slag, leaving the smelting slag entrapped by the casting slag.The casting slag dissolves and fluidifies the smelting slag as shown byan analysis of the slag in the ladle at the end of the pouringoperation. In the specific example referred to above, the smelting slagfrom the ferro-chromlum furnace had an analysis as follows:

Per cent S102 27.73 CaO 0.75 MgO 33.95 FeO 2.15 CrzOa 6.82 A1203 23.72

This slag was a very refractory, viscous slag. The slag in the ladle atthe completion of the This final ladle slag was a fairly fluid slag, itsviscosity ranging from 3.4 to 7 inches on the Herty viscosimeter. Itwill thus be seen that the body of slag, by dissolving and fluidifyingthe entering smelting slag, remains fluid through the entire castingoperation, thus minimizing the chance of inclusions that might otherwisebe entrapped in the metal as it passed through the slag. The fluidifyingof the smelting slag by its mixture with the casting slag releases metalshot which may be entrapped in the melting slag and thus increases theyield of ferro-chromium.

The thick layer of casting slag checks the velocity 0f the stream ofmetal poured from the furnace and causes a gentle descent of the metalonto the top of the pool of metal accumulating in the bottom of theladle. Any violent intermixing of the metal with the contents of theladle is thus avoided and the pool of accumulating metal is allowed toremain quiescent. The gently descending entering metal stream can havebut a limited penetration into the accumulating pool of ingot metal,thus shortening either the distance an entering particle of anynon-metallic substance must rise to meet the slag-metal interface incase it has evaded the filtering action of the'slag layer, or shorteningthe time required if it is released below that interface byprecipitation from the cooling metal.

The elimination of inclusions by the shortened distance of ascent to theslag-metal interface is helped by the slow cooling of the metal in ourprocess. Before the metal is tapped, the ladle is allowed to stand for.5 or minutes until the cast iron metal of the ladle is heated and untila chilled layer of insulating slag is formed over the bottom and sidesof the ladle, which prevents the pool of metal coming in direct contactwith the cast iron. This insulating layer of slag serves to keep themetal fluid for a longer period than where the metal is pouredimmediately into a cast iron ladle. The heavy body of slag on top of thepool of metal also serves to insulate it. Measurements of thetemperature of the ladle after pouring indicate that the freezing of themetal is considerably retarded and is not completed for some hours afterpouring, allowing the maximum time for inclusions to rise to the surfaceof the metal and thus be eliminated. These various factors combined inproducing in an enhanced degree a micrographic cleanliness in the metal,particularly with respect to non-metallic inclusions of a size order of200 microns or less, and more particularly 50 microns or less, which areso slow in rising through a column of liquid metal that they have beenentrapped in the highcarbon ferro-chromium ingots cast in the usualmanner.

After a cooling period of 6 to 8 hours the ladle is rip-ended and theentire cast skidded to the cleaning floor where the 12 to 15-inch toplayer of slag is easily split clean from the metal regulus, whosesurface is otherwise completely encased in a thin shell of chilled slag,usually between A; to inches in thickness, but occasionally reaching athickness of 1% inches, which peels off readily from the bright, smooth,dense ingot or regulus skin. The presence of the thin shell or skull ofslag over the sides and bottom of the regulus is evidence of theformation of such thin skull of slag during the period between thefilling of the ladle with the casting slag and the pouring of the metal,as otherwise the metal would freeze in contact with the cast iron bodyof the ladle.

The surface of the regulus is smooth and without sharp corners orprojections, showing that the metal solidified in an envelope of slag,which allowed the metal to slowly solidify and take on a rounded surfacecontour because of the action of the surface tension of the molten metalbefore solidification. This slow solidification allows the surface ofthe metal to free itself of surface inclusions of slag which have beencharacteristic of high-carbon ferro-chromium ingots as cast according tothe usual practice. When crushed the regulus is found free from pipe,gas holes or shrinkage cavities with a bright, lustrous, silveryfracture of remarkably even texture throughout, and a notable absence ofshrinkage strains is found, which ordinarily cause excessive shatteringand spalling, resulting in considerable loss microns or less in size andare principally of the duplex type, which are readily removable from thesteel to which ferro-chromium is added during the steelmaking process.Tests indicate that the ferro-chromium made according to our processcontains less than of l per cent of nonmetallic inclusions as determinedby acid dissolution, which is less than half of the content ofnon-metallic inclusions characteristic of highcarbon ferro-chromium madein the usual way. The nitrogen content of the ferro-chromium made by ourprocess has been found to be consistently lower of the order of A; ofthat of ferro-chromium cast in the ordinary way; for example, less than.025 per cent nitrogen as compared to the ordinary .06 to .10 per centnitrogen.

The polyhedral inclusions of the chromite type are claimed to beinsoluble in steelmaking slags at steelmaking temperatures up to 3100 F.and have created difiiculty in certain steelmaking processes, whereasthe small inclusions of the type which remain in our ferro-chromium arenot damaging to steels in that they are soluble in steelmaking slags atsteelmaking temperatures. The inclusions, therefore, are removable fromthe steel bath after the addition of form-chromium and during the courseof the steelmaking operation and, consequently, do not contaminate thesteel product as has been the case with the polyhedral inclusions of thechromite type. Such polyhedral inclusions are insoluble or for otherreasons not removed from the steelmaking slag and, therefore,contaminate the steel product. Such inclusions as remain in ourferro-chromium are of advantageous size and character and are eitherdissolved by the steelmaking slag or otherwise are removed in the courseof the steelmaking process and thus result in a steel product of a moredesirable character.

In the specific procedure above described, the pool of casting slag wasapproximately inches deep and the metal was poured from a height ofabout 3 feet. This depth of slag is sufficient to check and control thevelocity of the entering metal and to provide sufficient washing action.The depth of the casting slag may, however, be varied. The casting slagshould not be less than 60 about 12 to 15 inches thick in order to getproper control of the velocity of the metal and proper washing action.On the other hand, it is not necessary in general to increase the depthof the slag beyond about inches in orderto check 65 the velocity of themetal and get proper washing action, although the slag layer may besome-'- what deeper. Moreover, if the depth of the slag is too great,there is danger of granulation of the liquid metal, particularly if thetemperature of 70 the slag is lower than that of the metal.

The height of the pour will be governed some what by operativeconditions. We prefer to keep the height of the pour to a minimum; forexample, in the operation above described, the

75 height of pouring was inches. The height of aceasu pouring should notbe high enough so that the impact of the molten metal causes a turbulentintermixing of the metal and the contents of the ladle. In general.pouring above a height of or 6 feet should be avoided. In general. thehigher the height of pouring the deeper should be the layer of slag.The-depth of the slag and the height of pour should be so correlatedthat turbulent intermixing of the metal and contents of the ladle isavoided.

The thickness of the chilled skull of slag formed around the bottom andsides of the regulus depends on the mass and temperature of the metalladle or mold and the length of time between filling the ladle or moldwith the casting slag and the pouring of the metal describedspecifically above. The chilled layer or skull of slag should be thickenough to prevent the metal from coming into direct contact with theiron and to serve as an insulating layer between the iron of the mold orladle and the solidifying metal, which allows the surface tension of themolten metal to form a smooth skin and which also contributes to theslow freezing of the metal to give greater time for inclusions to riseto the top metal-slag interface. The skull of slag should be thin enoughso that it remains solid and its surface does not become too mushy orfluid in contact with the metal. If it is of too great a thickness, itwill not remain frozen under the heating of the metal by escape of theheat to the mold but the inner surface of such thick layer of slag willbecome quite mushy or even molten and the fingers of slag will extendinto and be entrapped within the metal surface. The ideal slag skinthickness appears to lie between and inch, although it may be as thickas 1 inch in some cases without harmful effect; in other cases,especially in small ingots, as thin as ,3 inch.

If desired, instead of pouring the metal into the casting ladle directlyfrom a smelting furnace, the metal can be tapped from a smelting furnaceor furnaces into a transfer ladle or ladles and poured into a castingladle or mold, thus producing a larger ingot or regulus when the metalis collected from two or more furnaces. In such case the smelting slagmay largely freeze in the transfer ladle so that the metal as teemedfrom the transfer ladle, particularly from a bottom pour ladle, may beaccompanied by little, if any, of the original smelting slag.

While it is much preferred to allow the metal to freeze into an ingot orregulus in the bottom of the ladle containing the casting slag, it ispossible to pour the molten metal accumulating beneath the casting slaginto a separate mold or molds before it freezes, obtaining some of theadvantages of increased micrographic cleanliness but to impaired degree,since we believe that it is highly desirable, if not necessary, inobtaining the full advantages of our invention to allow the metal tofreeze slowly enclosed in an envelope of casting slag.

We will now describe, as a second example, the application of ourprocess to the casting of low carbon ferro-chromium. The low carbonferrochromium was smelted in the usual way to produce a low carbonterm-chromium of the following composition:

Per cent Chromium 70.21 Silicon .68 Carbon .58

8 The heat weighed about 2,400 lbs. As poured from the furnace the metalhad a temperature of about 3130 degrees F. and the slag as poured fromthe furnace had a temperature of about 3100 degrees F. with a fluidityof 8 to 10 plus inches on the Herty viscosimeter.

The process as we carried it out is illustrated diagrammatically inFigure 2 of the drawings. The tilting smelting furnace is indicated atreference numeral I 0. A casting mold H was provided of the charactershown in the drawing. This mold consisted of a cast iron stool [2carried on a car l3 and a heavy mold frame or ring I of cast iron. Thestool I! was about six feet square outside dimensions and ten inches inthickness. The cast iron ring II had an inside dimension of aboutfifty-two inches square and a thickness of ten inches. The Joint betweenthe stool l2 and the ring M was luted with magnesite, as indicated at[5. Mounted on top of the ring I 4 was a cast iron ring or frame iswhich had a spout ll normally closed with a graphite plug l8. On top ofthe frame is there was a similar frame l9 provided with an overflowspout 20.

4 Each frame was about fourteen inches high and had an inside diameterof about fifty-two inches square. In carrying out our Process with thisapparatus as illustrated, the furnace was tilted and the greater part ofthe charge of smelting slag run into the composite mold which filled itto a depth of about twenty-five inches, the excess running out throughthe overflow spout 20. The pouring was then stopped for about fiveminutes to allow a thin layer of chilled slag to form against thesurface of the massive cold cast iron stool l2 and ring i4. After thisperiod of Walting, the furnace was tilted further and the metal pouredinto the mold through the layer of slag which was maintained at athickness of about twenty-five to nineteen inches, the excessoverfiowing through the spout 20. The metal formed a slab about sixinches thick in the bottom of the mold indicated by reference numeral 2l which was surrounded on its sides and bottom by a thin layer ofchilled slag 22. Within ten or fifteen minutes after the metal pour wascompleted, the plug l8 was removed and the lower side spout l1 tapped todrain the slag layer to a thickness of about six inches above the top ofthe metal, so that the metal might freeze quicker than with the originalthickness of slag. This slag discard left the hot top l6 at atemperature of about 2850 degrees F. and a fluidity of about 2% to 3%inches on the Herty viscoslmeter. In the course of five or six hours theingot was stripped from the mold and the layer of slag split from thetop of the ingot or regulus. The sides and bottom of the ingot orregulus were encased in a thin slag skin or skull about ya to V4 inch inthickness, which quickly disintegrated and crumbled from the ingot skinwhile the thick top layer would have required eight to twelve hours todisintegrate. The slab was afterward crushed in the usual way to formthe saleable low carbon ferro-chromium.

The action of the slag which was poured into the mold and allowed topartially chili before the metal was teemed was similar to thatdescribed in the first example except that in this case the smeltingslag was used as the casting slag since it did not have the highviscosity of the smelting slag in a high carbon ferro-chromium smeltingoperation. The slag, however, had the same action in washing theterm-chromium which passed through it and in checking the flow of andthe slag envelope served to surround the regulus as it froze and allowedthe surface tension of the metal to form a smooth, well-rounded skin asdescribed in connection with the first example. The ingots cast in thismanner had an equiaxial 1-2 millimeter granular crystal structurethroughout.

While the process has been carried out suc-' cessfully as abovedescribed, using the smelting slag as the casting slag, it is preferredto use a special casting slag which has a higher silica content and isfreer of iron and chromium oxides. Such slag is preferably prepared bytaking the smelting slag from a previous low carbon ferrochromiumsmelting operation and treating it with either chromium silicide orferro-silicon or aluminum to reduce and recover the chromium and ironoxide contents. An addition of silica sand is then made to the slag tomake it less basic and more fluid. A typical low carbon ferrochromiumsmelting slag had the following composition:

Per cent S102 28.55 (29.0 46.10 MgO 16.48 Feo 0.94 CrzOs 4.24 A1203 7.50Ratio CaO/SiOz 1.61

Such a slag after adjustment, as above described had approximately thefollowing analysis:

Percent SiO: 32.50 38.0 44.73 MgO 17.13 ZFeO .50 CrzOa 1.00 A1203 5.60Ratio CaO/SiOz 1.37

Such an adjusted slag instead of disintegrating and crumbling from theingot, formed a vitreous skin about to inch in thickness which shelledoff readily from the ingot skin as it cooled to atmospheric temperature.

The metal cast according to our method using either slag described aboveis characterized by an unusually brilliant, lustrous fracture with amarked improvement in macrographic and micrographic cleanliness andlowered nitrogen content as compared with low carbon ferro-chromium castby the ordinary methods. The ingot skin is smooth and bright as ifburnished, the burnished appearance being more pronounced, however, whenthe ingot is cast in the adjusted slag which forms a vitreous skin.

While the present invention has been developed and has been describedwith particular reference to the manufacture of high carbon and lowcarbon ferro-chromiums, our process is applicable to the treatment ofother refractory metals. By refractory metals we mean metals such aschromium, vanadium, titanium, zirconium, columbium, tantalum, uranium,etc. either in relatively pure form or in the form of alloys. Adistinguishing characteristic of such refractory metals is that theirreduction temperatures are higher than steelmaking temperatures, beingappreciably above 3000 F. Refractory metals are also characterized bythe presence of refractory high melting point viscous slags produced intheir smelting operations. Such slags tend to produce in the metalsrefractory high melting point inclusions which persist when the metalsare added to steels. The refractory metals to which this inventionrelates (and by "refractory metals" we mean to include their alloys) areused as intermediates in the metallurgical industry; especially, thoughnot exclusively, in steelmaking. Usually they are crushable and aresupplied in the crushed form in numerous size specifications. While suchmetals are used as intermediate alloys for steelmaking, they are alsoused in the non-ferrous industry as hardeners. Examples of refractorymetals particularly useful for the steelmaking industry are high-carbonferro-chromium, low-carbon ferro-chromium, ferro-silicon,ferrochromium-silicon, ferro-manganese, ferro-manganese-silicon,ferro-vana'dium (both low and high carbon with both high and low siliconcontent), as well as vanadium, chromium and titanium metals ofcommercial purity. When such refractory metals are treated with suitableslags, in accordance with our process, the advantages set forth ingreater detail in the above discussion of the manufacture of high-carbonand low-carbon ferro-chromiums are obtained.

Slags of the character above described can be used in the treatment ofsuch refractory metals. While we prefer for the sake of economy toemploy waste slags from other metallurgical operations adjusted to theproper fluidity, other slags may be used. The suitable slags may be, forexample, of either silicate or aluminate types, essentially calciumsilicates or aluminates, with relatively small amounts of otherslag-making oxides or they may be of compositions of the quaternarysystem, SlO2-AlzO3CaO-MgO, or in the three-component systems from whichit is constituted. The principal requirement is that the slag shalldevelop the proper fluidity, and 45 particularly a sufflciently highfluidity within the operating ranges of the pouring practice, and thatthe content of heavy metal oxides shall be low. namely under 5% andpreferably under 2%, in order to avoid reaction with the reducing ele-50 ments present in the metal being cast; this is especially desirableif a sound ingot or regulus, extremely low in its content of minutenonmetallic particles is to be obtained.

Slags containing sufficient lime and silica con- 5 tents may usually becaused to disintegrate into fine powder upon solidifying and cooling byadjusting their. composition to insure a substantial calciumortho-sillcate (2CaO.SiO2) component, while providing for the alumina aspentacalcium trialuminate (ECaOBAhOs) and the magnesia as Fosterite(2MgO.SiO2), adding 5 to 15% excess of the theoretrical limerequirements to insure rapid disintegration of the ingot slag skin uponstripping and cooling to atmospheric temperature.

By adjusting their composition in such a manner that a deficiency oflime exists, below the theoretrical requirements for 2CaO.SlOz afterother components are satisfied as above, the slag will not disintegrateupon cooling but will result in a cold-short, vitreous slag skin whichpeels readily from the ingot upon cooling below 800 to 900 F. .Thelatter type of casting slag is in many cases, though not necessarilyalways, more desirable from the standpoint of ingot metal qual- 76 ity.Calcium aluminate slags of the 5Ca0.3AlzOa type, with or without thepartial substitution of fluorspar up to 30 or 40% of their lime content,have been found to make excellent casting slags for chromium, vanadiumand titanium, aluminum-vanadium and aluminum-titanium as well as lowcarbon ferro-alloys of vanadium-titanium.

The cooling rate or freezing of the regulus or ingot can be varied andcontrolled in our process by the control of the depth of the castingslag pool as well as by the character of the molds themselves and by thetime allowed for the slag to heat the mold and to form an insulatingskull or skin. For example, in the above described procedure, in castingslabs of low carbon ferrochromium, it is possible by leaving on a heavylayer of casting slag, to cause the slab to crystallize largely, if notwholly, as columnar or prismatic dendritic crystals extending throughthe entire thickness of the slab. However, by tapping ofl the castingslag to leave a relatively thin layer and secure more rapid cooling ofthe slab, low carbon ferro-chromium can be made to crystallize entirelyin the form of. relatively small granular equiaxed crystals. The samecontrol of the crystalline qualities of the metal can be had with othermetals and alloys. Also, as described in connection with-the manufactureof high carbon ferro-chromium, the pouring of the slag into the moldfollowed by a period in which the slag heats the mold and forms aninsulating thin layer of slag along the bottom and sides of the mold,inhibits the formation of the initial thin skin of minute "chillcrystals" which are formed immediately upon contact of molten metalswith relatively cold walls of a chilled mold, and thereby permits thenatural forces of surface tension of the liquid metal to adjust the areaof its surface skin before solidification. When the initial chili isthus delayed, the sub-skin crystalline structure of the ingot may bemore readily controlled within wider limits as the rate of cooling isvaried by suitable ratio limits of the ingot surface area tocross-section, suitable limits of mold ratio (cross-sectional area ofthe mold per unit area of ingot) and correspondingly suitable heatdiffusivity Conductivity Specific Heat X Density of the superimposedlayer of casting slag and of the ingot mold. For example, in the castingof high carbon ferro-chromium as set forth in the specific exampleabove, the cast iron mold ladle weighed about 9,300 lbs. and wouldaccommodate an ingot as heavy as 6,300 lbs. at a chill ratio by weightof 1.48 and having a mold ratio ranging from .41 to .56, while the ratioof ingot surface to ingot cross-sectional area was 9.2. In the castingof low-carbon ferro-chromium with the arrangement shown in Figure 2, achill ratio as high as 10 or 12-1 may be used to advantage of optimummold life, with a mold ratio of .9 to 1.5.

Although we have specifically illustrated and described a preferredembodiment of our invention with particular reference to the making offerro-chromium, it is to be understood that the invention may beotherwise embodied and practised within the scope of the followingclaims.

We claim:

1. The process of casting high carbon ferrochromium which comprisesforming in a furnace a charge of molten ferro-chromium having the usualsupernatant viscous smelting slag, forming in a casting mold a body ofmolten casting slag at a temperature approximating that of the pouringtemperature of the ferro-chromium and considerably more fluid than thesmelting slag, allowing the casting slag to stand in the mold until athin skull of chilled slag forms against the bottom and sides of themold, pouring the molten ferro-chromium together with at least a part ofits smelting slag into the mold whereby the ferrochromium passes throughthe casting slag to form a. regulus in the bottom of the mold and thesmelting slag is entrapped by and dissolved in the casting slag, andallowing the ferro-chromium to solidify as a regulus in the bottom ofthe mold.

2. The process of casting refractory metals which have refractorysmelting slags characterized by high viscosity and from which the metalsdo not readily separate, which comprises forming in a casting mold abody of molten casting slag considerably more fluid than the smeltingslag and having a temperature sufficiently high so that the main body ofthe casting slag remains fluid during the metal pouring operation,allowing the slag to stand in the mold until a thin skull of chilledslag forms against the bottom and sides 01' the mold, and then pouringthe molten metal together with at least a part of its smelting slag intothe mold whereby the metal passes through the casting slag to form aregulus in the bottom of the mold and the smelting slag is entrapped byand dissolved in the casting slag, and allowing the metal to solidify asa regulus in the bottom of the mold.

3. The process of casting refractory metals which comprises forming in acasting mold a body of molten fluid casting slag at a temperature abovethe melting point of the metal to be cast and sufficiently high so thatthe main body of the slag remains fluid during the metal pouringoperation, allowing the slag to stand in the mold until a layer ofchilled slag forms against the bottom and sides of the casting moldsufficiently thick to form a slag skull around the bottom and sides ofthe metal regulus when cast of about one-sixteenth to one-half inchthick, pouring into the mold and through the body of molten casting slagthe metal to be cast without turbulent intermixing of the metal andslag, and allowing the metal to solidify in the mold to form a regulusenclosed in an envelope of slag.

4. The process of casting refractory metals which comprises forming in acasting mold a body of molten fluid casting slag at a temperature abovethe melting point of the metal to be cast and sufliciently high .toremain fluid during the metal pouring operation, allowing the slag tostand until a thin skull of chilled slag is formed over the bottom andsides of the mold, and then pouring into the mold and through the bodyof molten casting slag the molten metal to be cast so as to form-aregulus having a smooth skin, and

allowing the metal to solidify in the mold.

5. The process of casting low carbon ferrochromium which comprisesproviding a slab casting mold having heavy chilled bottom and sides,pouring into such mold a body of molten casting slag at a temperatureabove the melting point of the ferro-chromium to be cast andsufilciently high so that the main body of the slag remains fluid duringthe metal pouring operation, allowing the slag to stand in the molduntil a thin skull of chilled slag forms against the bottom and sides ofthe mold, pouring molten ferro-chromium into the mold and through thebody of casting slag without turbulent intermixing of the metal andslag, and allowing the metal to solidify in the 13 mold to form a slabsurrounded by an envelope of $188. V

6. The process of casting low carbon ferrochromium which comprisesforming in a casting mold a body of molten casting slag at a temperatureabove the melting point of the ferro-chromium and sufficiently high toremain fluid during the metal pouring operation, allowing the castingslag to stand in the mold until a thin skull of chilled slag formsagainst the bottom and sides of the mold, pouring the moltenferrochromium into the mold and through the body of casting slag andallowing the excess slag to be tapped from the mold, allowing the moldwith the casting slag to stand for a short time and thereafter tappingofi more of the casting slag, and allowing the ferro-chromium tosolidify in the mold. I

'1. A high carbon ferro-chromium regulus having a smooth, lustrousmetallic skin substantially devoid of chill crystallization and strainsresulting therefrom and of the character formed by the solidification ofsuch a regulus in an envelope of slag, the ferro-chromium containingless than 1/10 of 1% of non-metallic inclusions as determined by aciddissolution, said inclusions being predominantly 50 microns or less insize and being readily removable during the steel-making process fromsteel to which the ferro-chromium is added, the ferro-chromium beingsubstantially free of inclusions of the polyhedral refractory typecharacteristic of chromite.

8. As a new product of manufacture, high carbon ferro-chromiumconsisting of crushed reguli which has smooth, lustrous metallic skinssubstantially devoid of chill crystallization and strains resultingtherefrom and of the character formed by the solidification of such areguli in envelopes of slag, the ferro-chromium containing less than of1% of non-metallic inclusions as determined by acid dissolution, saidinclusions being predominantly 50 microns or less in size and beingreadily removable during the steel-making process from steel to whichthe ferro-chromium is added, the ferro-chromium being substantially freeof inclusions of the polyhedral refractory type characteristic ofchromite.

9. A regulus of refractory metal having a reduction temperatureappreciably above 3000 F., said regulus having a smooth, lustrousmetallic skin substantially devoid of chill crystallization and strainsresulting therefrom and of the character formed by the solidification ofsuch a regulus in an envelope of slag, the metal of said reguluscontaining less than 1 6 of 1% of non-metallic inclusions as determinedby acid dissolution, said inclusions being predominantly 50 microns orless in size and being readily removable during the steel-making processfrom steel to which the metal is added.

10. As a new product of manufacture, a refractory metal having areduction temperature appreciably above 3000 F., and consisting ofcrushed reguli whichhave smooth, lustrous metallic skins substantiallydevoid of chill crystallization and strains resulting therefrom and ofthe character formed by the solidification of such reguli in envelopesof slag, the metal containing less than 1 of 1% of non-metallicinclusions as determined by acid dissolution, said inclusions beingpredominantly microns or less in size and being readily removable duringthe steelmaking process from steel to which the metal is added, themetal being substantially free from inclusions of the refractory typecharacteristic of the smelting slags of such refractory metal.

, 11. A high carbon ferro-chromium regulus having a smooth, lustrousmetallic skin substantially devoid of chili crystallization and strainsresulting therefrom and of the character formed by the solidification ofsuch a regulus in an envelope of slag.

12. A regulus of refractory metal having a reduction temperatureappreciably above 3000 F., said regulus having a smooth, lustrousmetallic skin substantially devoid of chili crystallization and strainsresulting therefrom and of the character formed by the solidification ofsuch a regulus in an envelope of slag.

13. A regulus of refractory metal having a reduction temperatureappreciably above 3000 F., said regulus having a smooth, lustrousmetallic skin substantially devoid of chili crystallization and strainsresulting therefrom and containing less than of 1% of non-metallicinclusions as determined by acid dissolution, said inclusions beingpredominantly 50 microns or less in size.

14. The process of casting refractory metals which comprises forming ina casting mold a body of molten fluid casting slag, allowing the slag tostand until a thin skull of chilled slag is formed over the bottom andsides of the mold, then pouring molten metal into the mold through abody of molten casting slag, and allowing the metal to solidify in themold.

HOLBERT EARL DUNN.

HEINRICH WILHELM RATHMANN.

HOWARD CALVIN PARKMAN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 944,371 Monnot Dec. 28, 19091,753,891 Jones Apr. 8, 1930 2,445,670 Hopkins July 20, 1948 FOREIGNPATENTS Number Country Date 416,228 Great Britain Sept. 18, 1934

1. THE PROCESS OF CASTING HIGH CARBON FERROCHROMIUM WHICH COMPRISESFORMING IN A FURNACE A CHARGE OF MOLTEN FERRO-CHROMIUM HAVING THE USUALSUPERNATANT VISCOUS SMELTING SLAG, FORMING IN A CASTING MOLD A BODY OFMOLTEN CASTING SLAG AT A TEMPERATURE APPROXIMATING THAT OF THE POURINGTEMPERATURE OF THE FERRO-CHROMIUM AND CONSIDERABLY MORE FLUID THAN THESMELTING SLAG, ALLOWING THE CASTING SLAG TO STAND IN THE MOLD UNTIL ATHIN SKULL OF CHILLED STAG FORMS AGAINST THE BOTTOM AND SIDES OF THEMOLD, POURING THE MOLTEN FERRO-CHROMIUM TOGETHER WITH AT LEAST A PART OFITS SMELTING SLAG INTO THE MOLD WHEREBY THE FERROCHROMIUM PASSES THROUGHTHE CASTING SLAG TO FORM A REGULUS IN THE BOTTOM OF THE MOLD AND THESMELTING SLAG IS ENTRAPPED BY AND DISSOLVED IN THE CASTING SLAG, ANDALLOWING THE FERRO-CHROMIUM TO SOLIDIFY AS A REGULUS IN THE BOTTOM OFTHE MOLD.